<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>

    <style>
      .box {
        height: 400px;
        width: 300px;

        background-image: radial-gradient(red, yellow, green);
      }
    </style>
  </head>
  <body>
    <div class="box"></div>
  </body>
</html>
